1. Technical Field of the Invention
The present invention relates generally to controlling the pressure load on various members, and more particularly to the active control of pressure loads using porosity.
2. Discussion of the Related Art
Pressure loading of a member can be caused by movement of the fluid and/or the member relative to one another. For example, many portions of an aircraft such as its forebody, canopy, fuselage, wings and tails are subjected to high air loads during flight. These air loads can vary significantly with model attitude and forward flight speed. Of particular concern for high performance military aircraft is that, depending on the geometry of the aircraft and its angle of attack, it may experience a large side force which results in a yawing moment which may be difficult to control. At low angles of attack the flow field is usually symmetric. As the angle of attack increases, two counterrotating, stationary vortices form on the leeward side of the forebody of the aircraft. At higher angles of attack, the vortices become asymmetric creating greater pressure on one side of the aircraft forebody than the other thus resulting in a net side force and yawing moment. If not controlled, the resultant force and moment on the vehicle can be extreme and create an unsafe condition or significantly reduce the flight envelope of the aircraft.
Likewise, many helicopter components such as the tailboom, helicopter body, rotor hub and the rotor itself bear high loads. Land based vehicles such as cars, trucks, vans and especially tractor trailers often encounter huge loads due to inadequate front, top and rear designs. Also buildings, in particular roofs, are exposed to loads from wind conditions which can cause undue strain and even catastrophic failure.
Numerous solutions have been proposed for controlling pressure load which are usually member specific. Initial design of the exterior of the member is an important consideration but is unable to adapt to changing loading conditions. Mechanical devices such as strakes and flaps are often used on vehicles to effectively alter the exterior surface of the vehicular member to achieve a desired reaction to loading. Also various air loading displacement systems are used which suck air from a high pressure area and/or forcibly exit air at a low pressure area to compensate for load induced pressure gradients. These mechanical devices and displacement systems are relatively complicated, have significant energy requirements, add weight to the vehicle, consume often critical space, and are often ineffective over a wide range of angles of attack and lift conditions. Most attempts to reduce air loading on buildings involve initial exterior design as well as flexible internal structure which yields slightly to wind loads.
It is accordingly an object of the present invention to control pressure loading on members.
It is another object of the present invention to control pressure loading over a wide range of member attitude and free stream flow conditions.
It is another object of the present invention to achieve the foregoing objects with a simple control device using minimal energy.
It is a further object of the present invention to achieve the foregoing objects with minimal spatial and mass requirements.
It is yet another object of the present invention to accomplish the foregoing objects in a simple manner.
Additional objects and advantages of the present invention are apparent from the drawings and specification which follow.